1. Field of the Invention
This invention relates to a process for continuously separating uranium isotopes by oxidation-reduction reaction using an anion exchanger. More particularly, it relates to a process for efficiently regenerating the deactivated oxidizing agent in the course of the separation of uranium isotopes by oxidation-reduction reaction, followed by reusing the regenerated oxidizing agent for continuing the separation of uranium isotopes.
2. Description of the Prior Art
According to one conventional process for separating uranium isotopes by oxidation-reduction reaction using an anion exchanger, a solution containing an oxidizing agent capable of oxidizing uranium (IV) to uranium (VI) is supplied to a developing column packed with an anion exchanger to form an oxidizing agent adsorption zone, followed by supplying a uranium isotope solution containing uranium (IV) to convert a portion of the oxidizing agent adsorption zone to an adsorbed uranium (VI) zone and then supplying a solution containing a reducing agent capable of reducing uranium (VI) to uranium (IV) to reduce uranium (VI) absorbed on the anion exchanger to be eluted in the form of uranium (IV).
Thus, a boundary is formed between the oxidizing agent zone and the uranium adsorption zone in the front portion, in the direction of flow, of the uranium adsorption zone, and the uranium solution recovered from the vicinity of this boundary has a higher concentration of uranium-238. Also a boundary is formed between the uranium adsorption zone and the reducing agent zone in the rear portion, in the direction of flow, of the uranium adsorption zone, and the uranium solution recovered from the vicinity of this boundary has a higher concentration of uranium-235.
In this separation of uranium isotopes it is also known that more than one developing column filled with an anion exchanger may be employed, and the eluted solution containing uranium (IV) is fed from one developing column to the next packed with an anion exchanger where an oxidizing adsorption zone is already formed, thereby continuously forming a uranium adsorption zone, and then passing a solution containing a reducing agent therethrough.
These operations of separating uranium isotopes are so-called fixed bed type operations of separating uranium isotopes.
According to another conventional process for separating uranium isotopes by oxidation-reduction reaction using anion exchanger, which is a so-called moving bed type operation, an anion exchanger having adsorbed an oxidizing agent thereon is supplied to a developing column where a uranium adsorption zone is already formed, and at the same time a solution containing a reducing agent is supplied to the developing column counter-currently to the flow of the anion exchanger, thereby performing oxidation and reduction reactions at the boundary between the uranium adsorption zone and the oxidizing agent and at the boundary between the uranium adsorption zone and the reducing agent, respectively. According to this moving bed type operation, the uranium adsorption zone is in a standstill state in a developing column by moving an anion exchanger in contrast to the uranium adsorption zone which moves in a developing column according to those fixed bed type operations. However, the principle of separating uranium isotopes is the same in the operations of the both types, and a deactivated oxidizing agent and a deactivated reducing agent are eluted as a mixture from a developing column in the operation of the both types.
In these operations uranium atoms should be in an anionic form. Uranium ion which is not coordinated with a ligand is usually in a cationic form. Thus, a uranium cation is converted to a uranium anion by forming complex compounds with negatively charged ligands. As used herein and in the appended claims, the term "uranium (IV)" denotes all tetravalent uranium ions including complex ions, and the term "uranium (VI)" denotes all hexavalent uranium ions including complex ions.
Heretofore, the deactivated oxidizing agent and the deactivated reducing agent which are present as a mixture in the eluant from a developing column are firstly separated from each other by a separator such as an extracting means, a column packed with an ion exchange resin, a precipitating vessel, etc. Secondly, the deactivated oxidizing agent thus separated is regenerated using another oxidizing agent such as oxygen, and on the other hand the deactivated reducing agent is regenerated using another reducing agent such as hydrogen, and the regenerated oxidizing agent and reducing agent are reused, respectively, for further separation of uranium isotopes by oxidation-reduction reaction.